Heating, ventilation and air conditioning systems use ventilation air ducts installed throughout a building to supply conditioned air to a room through outlet vents, and ducts to remove air through return grilles. Galvanized mild steel is the standard and most common material used in fabricating ductwork. For insulation purposes, metal ducts may be lined with faced fiberglass blanket (duct liner) or wrapped externally with fiberglass blankets (duct wrap), or lined or wrapped with foams or other insulative materials.
Traditionally, air ductwork was made of sheet metal which was installed first and then lagged with insulation as a secondary operation. Aluminum tape was applied to all seams where the external surface of the aluminum foil had been cut. Internal joints then could be sealed with a sealant.
When used outside, the ductwork and insulation combined therewith require a weather tight seal. U.S. Pat. No. 6,360,783 discloses one improved duct work system in which insulating panels are applied externally around the metal duct. The insulating panels comprise two adjacent insulation panels. Then, an embossed metal layer extends over the outer surfaces of the outermost insulation panel. Adjacent insulating panels are joined by fasteners. The embossed metal layers overlap at some edges and are further joined by grout or adhesive to create moisture barriers at their overlapping edges and interfaces.
Ducting systems that use insulation panels to form the ductwork passageway without an inner sheet metal duct have been proposed for indoor use. Such systems lack stability and weather resistance necessary for exterior ductwork systems. Accordingly, improvements to ductwork systems and more weather-robust exterior ductwork systems continue to be sought.